For Spirits when they please Can either sex assume, or both; so soft And uncompounded is their essence pure, Not tied or manacled with joint or limb, Nor founded on the brittle strength of bones, Like cumbrous flesh; but in what shape they choose Dilated or condensed, bright or obscure, Can execute their airy purposes, And works of love or enmity fulfil.
It is worthy of notice that Apollonius nowhere introduces the notion of directrix for a conic, and that, though he incidentally discovered the focus of an ellipse and hyperbola, he did not discover the focus of a parabola. Conspicuous in his geometry is also the absence of technical terms and symbols, which renders the proofs long and cumbrous.Florian Cajori
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